Implementation and performance of a fiber-coupled CMOS camera in an ultrafast reflective high-energy electron diffraction experiment

The implementation of a monolithic fiber-optically coupled CMOS-based TemCam-XF416 camera into our ultra-high vacuum (UHV) ultrafast reflection high-energy electron diffraction setup is reported. A combination of a pumpable gate valve and a self-built cooling collar allows UHV conditions to be reached without the need to remove the heat-sensitive device. The water-cooled collar is mounted to the camera housing and prevents heating of the camera upon bakeout of the UHV chamber. The TemCam possesses an one order of magnitude higher spatial resolution, which provides 30% higher resolution in reciprocal space than the previously used microchannel plate detector. The low background intensity and the four times larger dynamic range enable analysis of the diffuse intensity of the diffraction pattern like Kikuchi lines and bands. A key advantage over the previous MCP detector is the complete absence of the blooming effect, which enables the quantitative spot profile analysis of the diffraction spots. The inherent light sensitivity in an optical pump experiment can be overcome by subtracting a pump image without a probe, using photons with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>h</mml:mi> <mml:mi>ν</mml:mi> <mml:mo><</mml:mo> <mml:mn>1.12</mml:mn></mml:mrow> </mml:math> eV (indirect bandgap of silicon), or shielding any stray light.